Chiffchaff ?

This little bird visited the garden this afternoon, I believe it to be a juvenile Chiffchaff rather than a Willow Warbler, but I stand to be corrected!   I made this assumption due to the thin blackish legs and the thin beak.   A good day in the garden tidying flower beds and the patio area, but rain stopped play late afternoon.    I had a little Robin for company but when I tried to take a photograph of him he became camera shy and disappeared, I haven't seen him since!